A research program was carried out to investigate the residual compressive strength of high-porformance concrete (HPC) and normal strength concrete (NSC) after they were exposed to high temperatures, 8O0℃ and 1100℃, and two cooling regimes, Test results obtained showed that eompared with the strength at room temperature, the residual strength of both HPC and NSC dropped sharply after exposure to high temperatures. Water cooling, which resulted in a significant thermal shock. caused a bit more severn deterioration in strength compared to furnace cooling. Thermal shock was not necessarily the primary cause for spalling in HPC. Mereury intrusion porosimetry tests were carried out to measure variation in the pore structure of concrete. Sigaifieant changes in the cumulative pore volume curves before and after high lemperatures in both NSC and HPC were observed. The cumulative pore votume of HPC increased more remarkably than thai of NSC. The difference between the effects of the two cooling regimes on mechanical property as well as the microstmeture decreased at 1100℃ when compared 800℃.